In engine fuel delivery systems of current design, fuel is typically fed by a constant-delivery pump from a fuel tank to the engine. A pressure regulator maintains constant fuel pressure at the engine, and excess fuel is returned from the engine to the fuel tank. Such return fuel carries engine heat to the fuel supply tank, and consequently increases temperature and vapor pressure in the fuel tank. Venting of excess vapor pressure to the atmosphere not only causes pollution problems, but also deleteriously affects fuel mileage. Excess fuel tank temperature can also cause vapor lock at the pump, particularly where fuel level is relatively low. Constant pump operation also increases energy consumption, while decreasing both fuel pump life and fuel filter life. It is therefore desirable not only to eliminate the necessity for the fuel return line from the engine to the supply tank (while still maintaining constant fuel pressure at the engine), but also to control pump operation as a function of fuel requirements at the engine both to maintain constant fuel pressure at the engine and to increase pump life.
U.S. Pat. No. 4,728,264 discloses a fuel delivery system in which a d.c. motor fuel pump delivers fuel under pressure from a supply tank to an engine. A pressure-sensitive switch, which may be contained within a unitary pump/motor housing, is responsive to fuel pump output pressure for applying a pulse width modulated d.c. signal to the pump motor, and thereby controlling pump operation so as to maintain constant pressure in the fuel delivery line to the engine independently of fuel demand. U.S. Pat. No. 4,789,308 discloses a self-contained fuel pump that includes an electronic sensor in the pump outlet end cap responsive to fuel outlet pressure for modulating application of current to the pump motor and maintaining a constant pressure in the fuel delivery line to the engine. Copending U.S. application Ser. No. 07/421,810 filed Oct. 16, 1989 discloses a fuel delivery system that includes a unitary fuel pump assembly in which a pressure sensor is coupled to the pump outlet port for measuring fuel delivery pressure. A second sensor is positioned within the fuel tank and is responsive to fuel alcohol concentration. A circuitboard assembly on the pump outlet end cap receives the signals from the pressure and alcohol sensors, and supplies a pulsed d.c. signal to the pump motor having a duty cycle that varies as a combined function of the pressure and alcohol concentration sensor output signals so as to maintain constant fuel pressure at the engine while automatically compensating quantity of fuel delivered by the pump for differing fuel alcohol concentrations. The noted patents and application are all assigned to the assignee hereof.
Although the fuel delivery systems and pumps disclosed in the noted patents and application address and overcome a number of problems theretofore extant in the art, further improvements remain desirable. For example, the preferred embodiments of the pumps disclosed in the noted patents and application employ brush-type d.c. motors with associated commutator brushes and springs for urging the brushes into engagement with the rotating armature. These brushes are subject to wear and failure. It is therefore a general object of the present invention to provide a self-contained electric-motor fuel pump that includes a brushless-type d.c. motor and associated drive electronics with on-board outlet pressure compensation.